Spent selective catalytic reduction catalyst secondary resource
Used vanadia-tungsta/titania catalysts from coal-fired power-plant flue-gas denitrification, represented by separately characterized laboratory feeds. Niu and colleagues studied an arsenic-contaminated honeycomb catalyst from a Xinjiang plant; Su and colleagues separately studied gray and yellow regions of three spent honeycomb catalysts, S3–S5. This manufactured, heterogeneous secondary resource is distinct from refinery hydroprocessing, fluid catalytic cracking and sulfuric-acid-production catalysts, pure constituent oxides, mineral species and elemental vanadium or tungsten. V2O5-WO3/TiO2 is the sources' catalyst formulation notation, not proof of three separately quantified crystalline phases. Fresh catalysts S1–S2 in Su's study are comparators, not spent-resource observations. No criticality designation is inherited from the constituents.
Microbial & Biochemical Mechanisms (2)
Extracellular bioacid leaching of arsenic before catalyst regeneration
bioleaching
Microbial
Associated Organisms:
Acidithiobacillus thiooxidans ATCC 19377 (NCBITaxon:637390)
Acidic culture supernatant produced by source-reported Acidithiobacillus thiooxidans ATCC 19377 leached arsenic from a ground spent SCR catalyst. This demonstrates treatment by a microbial lixiviant after cell and sulfur separation, not direct growing-cell attack on the catalyst. Concentrating the supernatant improved arsenic removal in the tested conditions. Subsequent vanadium/tungsten supplementation, drying and calcination formed a separate regeneration stage before laboratory NO-conversion tests. These results do not demonstrate isolated arsenic recovery or an industrial regeneration operation.
Experimental Context & Analytical Limits:
Niu2025 Methods 1.1–1.4: the Xinjiang coal-power-plant catalyst was ground and sieved to at most 0.25 mm. A logarithmic-phase culture was inoculated at 5% vol/vol into modified mineral medium with 20 g sulfur per liter, initial pH 2.0–2.5, and grown at 32 +/- 1 degrees C and 150 rpm for 6–8 days until pH 0.8. Centrifugation at 7012 g for 10 minutes removed cells and sulfur; the supernatant was designated Ats. C-Ats was prepared by rotary evaporation from 1 liter to 500 mL, a twofold volume concentration called single concentration in the source. Leaching used 100 mL liquid in 250 mL flasks. The selected C-Ats treatment used 5% mass/volume solids, initial pH 0.6, 50 degrees C, 150 rpm and 8 h. The pH-adjustment reagent and independent verification of supernatant sterility were not specified. Liquid samples were centrifuged and filtered at 0.22 micrometers before ICP-OES. Source tables give means +/- standard deviations, n=3; leaching percentages use initial feed element inventory as denominator. No complete solids/liquids balance, isolated metal product, detection limit for reported zero tungsten loss or long-term reuse cycles were demonstrated.
Niu2025 Methods 1.1–1.4: the Xinjiang coal-power-plant catalyst was ground and sieved to at most 0.25 mm. A logarithmic-phase culture was inoculated at 5% vol/vol into modified mineral medium with 20 g sulfur per liter, initial pH 2.0–2.5, and grown at 32 +/- 1 degrees C and 150 rpm for 6–8 days until pH 0.8. Centrifugation at 7012 g for 10 minutes removed cells and sulfur; the supernatant was designated Ats. C-Ats was prepared by rotary evaporation from 1 liter to 500 mL, a twofold volume concentration called single concentration in the source. Leaching used 100 mL liquid in 250 mL flasks. The selected C-Ats treatment used 5% mass/volume solids, initial pH 0.6, 50 degrees C, 150 rpm and 8 h. The pH-adjustment reagent and independent verification of supernatant sterility were not specified. Liquid samples were centrifuged and filtered at 0.22 micrometers before ICP-OES. Source tables give means +/- standard deviations, n=3; leaching percentages use initial feed element inventory as denominator. No complete solids/liquids balance, isolated metal product, detection limit for reported zero tungsten loss or long-term reuse cycles were demonstrated.
Curated Evidence Points:
Support
Source:
niu2025
Table 7 and section 2.3.5 report 81.63 +/- 2.51% arsenic leaching for C-Ats versus 44.74 +/- 2.94% for Ats at the stated selected conditions. Ats plus 1 g/L ascorbic acid gave 46.90 +/- 2.30%, and Ats plus 1 g/L humic acid gave 45.57 +/- 3.10%; those small differences alone do not establish separate reduction or chelation mechanisms. All four entries report tungsten loss as zero, with no assay detection limit. The claim of residual arsenic below 200 g/t is stated in the abstract and conclusion without a separate residual-solid assay or solids mass balance being presented.
Partial
Source:
niu2025
Table 2 and section 2.2 compare 8 h, 50 degrees C, 5% mass/volume assays. Ats, sulfuric acid and oxalic acid started at pH 0.8; the alkaline comparator was 2% NaOH. Arsenic leaching was 35.30 +/- 1.47%, 1.50 +/- 0.70%, 20.55 +/- 1.83% and 80.62 +/- 3.74%, respectively. Tungsten losses were reported as zero, zero, 3.81 +/- 0.31% and 28.93 +/- 0.44%. Thus the alkaline arm removed more arsenic but lost more tungsten; the abstract's unqualified superiority claim for bioacid is not adopted. These chemical comparators do not include uninoculated culture medium processed and concentrated identically. They do not isolate the contributions of acidity, medium constituents and metabolites.
Partial
Source:
niu2025
Sections 2.2–2.3 propose thiol-containing microbial metabolites attacking arsenic-oxygen bonds, citing earlier Niu2021 work. This paper does not directly identify or quantify those metabolites or demonstrate the proposed molecular reaction. Its explanation that decreasing pH promotes thiol deprotonation is not adopted as established chemistry. Tables 3–6 retain the condition dependence: higher solids loading lowered extraction, while 65 degrees C and 10 h individually gave more extraction than the selected 50 degrees C and 8 h conditions. The selected condition is not an unconstrained maximum. Repeated 44.74% Ats means have different reported standard deviations across Tables 3–7 and are not treated as a pooled estimate.
Support
Source:
niu2025
Methods 1.5–1.6 and Figure 3 distinguish spent catalyst, spent catalyst supplemented with V/W, and bioacid-treated catalyst supplemented with V/W. The last arm reached source-reported 100% NO conversion at 300 degrees C in a fixed-bed test using 0.1 g of 40–60 mesh material, 100 mL/min total gas, 5% oxygen, 0.1% each NH3 and NO, and nitrogen balance. No bioacid-only NO-conversion curve is supplied. The supplementation recipe omits exact loading amounts and final calcination temperature; drying was 110 degrees C for 6 h, followed by a 5 degrees C/min ramp and 3 h hold at the unspecified setpoint. Figure 2 shows anatase-like diffraction patterns before and after treatment; missing V2O5/WO3 peaks do not establish quantitative phase purity. No independently verified industrial reuse standard or field deployment is asserted.
Context_only
Source:
niu2025
Table 1 identifies V, W, Ti, Ca, Fe and As in the studied feed and reports arsenic as 986.7 +/- 2.1 g/t. The Ti(K), Ca(K) and W(K) headings have an unexplained K designation under a common g/t unit, including Ti(K) 664.3 +/- 2.3. Those ambiguous entries are not converted into a normalized composition or reconciled by assumption. The industrial origin of the feed does not establish industrial use of the microbial treatment.
Context_only
Source:
ncbi_atcc19377
The official entry resolves the exact ATCC 19377 taxon designation used in Methods 1.2. It supplies identity context only; no genome or independently authenticated experimental strain is inferred.
Chemical alkaline leaching of vanadium and tungsten from spent SCR regions
separation
Sodium hydroxide transferred vanadium and tungsten from separately prepared yellow and gray regions of spent SCR catalysts into solution. The direction of the color-region difference was opposite for the two elements: yellow regions gave more vanadium extraction and gray regions more tungsten extraction. This is a separate abiotic laboratory study, not a control arm of Niu2025 or evidence of microbial metal recovery.
Experimental Context & Analytical Limits:
Su2020 Methods 2.1–2.3: only catalysts S3–S5 were spent; S1–S2 were fresh. Deposited solids were removed with 0.5 MPa compressed air, yellow and gray regions were manually separated, transition regions discarded, and samples hammered, vibration-milled, dried and sieved to less than 100 mesh. Methods specify 1.5 mol/L NaOH, 100 degrees C, liquid/solid ratio 15 with no explicit unit, 900 rpm and 120 minutes in a 50 mL Teflon tube in an oil bath; the conclusion instead states 240 minutes. That unresolved duration conflict prevents treating either value as uniquely verified. Actual liquid volume and solid mass are not given. Filtered leachates were analyzed by ICP-OES; feed V/W inventories were corrected using wet digestion rather than taken directly from XRF. Replicate counts and uncertainty for the plotted extraction percentages were not supplied.
Su2020 Methods 2.1–2.3: only catalysts S3–S5 were spent; S1–S2 were fresh. Deposited solids were removed with 0.5 MPa compressed air, yellow and gray regions were manually separated, transition regions discarded, and samples hammered, vibration-milled, dried and sieved to less than 100 mesh. Methods specify 1.5 mol/L NaOH, 100 degrees C, liquid/solid ratio 15 with no explicit unit, 900 rpm and 120 minutes in a 50 mL Teflon tube in an oil bath; the conclusion instead states 240 minutes. That unresolved duration conflict prevents treating either value as uniquely verified. Actual liquid volume and solid mass are not given. Filtered leachates were analyzed by ICP-OES; feed V/W inventories were corrected using wet digestion rather than taken directly from XRF. Replicate counts and uncertainty for the plotted extraction percentages were not supplied.
Curated Evidence Points:
Support
Source:
su2020
Figures 2–3 and section 3.1: for spent S3, S4 and S5, yellow/gray vanadium leaching percentages were 66.8/42.1, 68.8/40.0 and 67.7/49.0, respectively; tungsten percentages were 38.0/44.6, 52.6/57.3 and 44.7/53.2. These are feed-inventory-normalized dissolved fractions, not product purity or isolated recovery yields. Fresh S1–S2 results and the prior studies summarized in Table 1 are not assigned to the spent-feed experiment.
Partial
Source:
su2020
Table 2 gives oxide-equivalent bulk composition, not mineral-phase fractions. Figure 4 identifies anatase diffraction and notes that undetected V/W phases may be noncrystalline or below detection. Figures 5–9 and Table 4 support associations with surface composition, fitted V oxidation-state fractions and V-W-Ti interactions. The proposed causal explanations for color-dependent extraction were not independently isolated experimentally. Different source feeds, surface sampling and preparation constrain generalization. No downstream V/W product isolation or industrial leaching campaign was reported.
Sources & References
-
niu2025: Niu T, Xie X, Zhang X, Ma X, Feng F, Liu D and Tian B (2025). Mild Extraction and Green Regeneration of Arsenic from Spent SCR Catalysts. Nonferrous Metals (Extractive Metallurgy), issue 12:38–45. DOI 10.20237/j.issn.1007-7545.2025.12.004. Complete official eight-page Chinese-language article with English abstract; Methods 1.1–1.6, Tables 1–7 and Figures 1–3. DOI resolves through the Chinese DOI registration service; Crossref lookup returned 404.
https://doi.org/10.20237/j.issn.1007-7545.2025.12.004 (accessed 2026-10-12) -
niu2025_official: Official journal landing page and linked complete original PDF for Niu and colleagues (2025), article 526345ce1bab0e280b71bb99e0bb1f12. Title, authors, DOI and 2 December 2025 publication date agree with the registered citation; this is the same experiment, not another study.
https://mete.cbpt.cnki.net/portal/journal/portal/client/paper/526345ce1bab0e280b71bb99e0bb1f12 (accessed 2026-10-12) -
su2020: Su Q, Yi X, Miao J, Chen Y, Chen J and Wang J (2020). A Comparative Study in Vanadium and Tungsten Leaching from Various Sources of SCR Catalysts with Local Difference. Sustainability 12(4):1499. DOI 10.3390/su12041499. Complete official twelve-page PDF and XML; Methods 2.1–2.4, Figures 1–9 and Tables 1–4. Spent-feed evidence is restricted to S3–S5.
https://doi.org/10.3390/su12041499 (accessed 2026-10-12) -
ncbi_atcc19377: NCBI Taxonomy 637390, Acidithiobacillus thiooxidans ATCC 19377; exact strain-labelled taxon checked 12 October 2026. This resolves the designation reported by Niu2025; it is not independent authentication or sequencing of that study's culture.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=637390&mode=Info (accessed 2026-10-12)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-12T13:23:23Z |
codex (GPT-6; codex) | CREATE | Created a distinct spent SCR catalyst resource from complete official Niu2025 and Su2020 originals. Separated microbial bioacid arsenic removal, subsequent catalyst regeneration and abiotic spent-feed V/W extraction; retained control, detection-limit, composition and duration conflicts. Deferred unavailable earlier microbial originals. Independent review is recorded separately. |
Record source: data/records/spent-selective-catalytic-reduction-catalyst.yaml